Implant preparations containing bioactive macromolecule for sustained delivery

ABSTRACT

Implant preparations capable of sustained action when inserted are comprised of powder of a natural lipoidal substance in thorough admixture with bioactive macromolecule, followed by compression under pressure into a disc or rod that can be broken and used in small pieces as well.

This is a continuation-in-part of application Ser. No. 16,845, filedFeb. 20, 1987 and now abandoned.

FIELD OF THE INVENTION

This invention relates to bio-absorbable implant preparations containingbioactive macromolecule, which are capable of sustained action whenimplanted.

BACKGROUND OF THE INVENTION

Drug administration by the oral route is applicable mostly to lowmolecular weight (<850 daltons) compounds which are relatively stable atthe acidic pH of the stomach and the alkaline condition of thegastrointestinal tract. Bioactive macromolecules, such as insulin (Mol.Wt. 6,000 daltons) which promote growth and control blood sugar level,and the growth hormone somatotropin (Mol. Wt. 22,000 daltons) or thelike are inactivated by proteolytic enzymes in the digestive tract, iftaken by mouth. As a result, these bioactive macromolecules can beadministered only by injection. However injection usually introduces toohigh an initial dose which is absorbed in part as well as degraded byserious enzymes at the subcutaneous injection site resulting in rapiddecay to an inadequately low level a few hours later. To compensate forthe decay, a second injection is required. Another remedy to correct theinconsistency is to infuse dilute solution of the labile agentcontinuously at a low rate. The slow infusion can actually achieve abetter outcome, because most active agents have relatively shorthalf-life in vivo or are toxic if the daily required dose is given atonce by injection. However, the advantage of low-dose infusion iscompromised by the incidence of infection and discomfort due to thepresence of the indwelling needle and the catheter attachment.Therefore, extensive effort is continuing to find an implantableinfusion device or preparation that can deliver an active agent for aprolonged period of time.

BRIEF REFERENCE TO THE PRIOR ART

In the early 1970's when the merit of giving a drug in small doses bycontinuous external infusion was demonstrated, further efforts wereaimed at the development of implantable pumps and drug releasingcapsules to simulate the functions of organs such as the hormonesecreting endocrine glands. Another purpose was to free the recipient ofthe chance of infection and provide total unrestrained mobility whichoften contributed immensely to the patient's sense of well being.

There is one implantable pump available commercially at present (theInfusaid® Implantable Pump manufactured and marketed by the InfusaidCorporation, Norwood, MA). This titanium device weighs about 200 g, hasa drug solution reservoir capacity of about 40 mL and is powered by avolatile fluorocarbon propellant which exerts a constant pressure on thecollapsible drug solution reservoir. The liquid is driven through alength of resistive capillary coil to deliver the solution at a flowrate of about 5 mL/day. In about a week, the reservoir must be refilledpercutaneously, and drug spilling into the subcutaneous space occurredfrequently. Further, this implantable pump can be used only with activeagents that are soluble in aqueous buffer solutions, stable at bodytemperature, and do not form aggregates which will clog the filter orthe flow-regulating resistive capillary of the pump.

In the past six years, experience has shown that this device worksrelatively well with low molecular weight drugs, such as morphine (Mol.Wt. 285), 2'-deoxy-5-fluorouridine (Mol. Wt. 246) or the like in thetreatment of cancer patients at a relatively advanced state of thedisease. For macromolecular weight drugs, this pump also works quitewell with the heparin anticoagulant, however polypeptide hormones, suchas insulin and somatotropin or the like, have limited solubility andhave a high tendency to form aggregates after a few days in solution.Therefore, the implantable pump is not suitable for these polypeptidehormones.

There have been several different designs of implantable pump underdevelopment during the past five years. These experimental prototypesall use electrically powered roller pumps to propel the liquid from thesolution reservoir. Because the maximum size of a subcutaneous implantis about 9 cm in diameter by about 3 cm in thickness, the space taken upby the electrical and mechanical components forced the reduction of thereservoir volume to less than 30 mL, which necessitates more frequentrefilling. Further, moisture penetration due to sealing defects of themetallic enclosure often led to short circuiting and pump failure.Therefore, despite extensive effort over the past several years, theInfusaid® implantable pump remains the only one commercially available.It is apparent that drug delivery by implantable pumps has reached closeto the limit of feasibility.

In a quite different approach, many existing and specially synthesizedpolymers have been evaluated for suitability as excipient for drugdelivery implants. The advantages of such an implant are its relativelysmall size as compared to the pumps aforementioned, and the fact thatthe active agent can be compounded with the excipient material directlyin an amount without dilution which often lasts for months or evenyears. The implant which has received extensive evaluation is thecontraceptive silicone capsule containing norgestrel having a molecularweight of 312 daltons. This low molecular weight steroid can penetratethe silicone material continuously to prevent pregnancy for up to 5years (H.B. Croxatto, et al., Contraception, 23, 1981, 197). However,the fibrous tissue encapsulation developed in time around the implantmakes its removal extremely difficult. For this reason, and also becausebioactive macromolecules cannot penetrate the silicone rubber, furtherefforts have been directed at the development of excipients that can beeroded and gradually absorbed in the body (J. Heller in Recent Advancesin Drug Releasing Systems, Anderson & Kim (eds) Plenum Press, 1984,N.Y., p.101). The erosion will also allow the leaching out of bioactivemacromolecule incorporated therein, and make the removal laterunnecessary.

Several synthetic polymers, notably poly-(alkyl-α-cyanoacrylate),polyurethanes, and polyesters are known to degrade to some extent andbecome absorbed once implanted in the body. However, because of thelimited possibility of controlling the biodegradation rate as well asthe toxic degradation products formed, especially bypoly-(alkyl-α-cyanoacrylate) and polyurethane, the current search for abiodegradable drug delivery implant has concentrated almost exclusivelyon different kinds of polyester as the excipient material. Often, thenovel polyesters erode too slowly in the aqueous environment, and as aresult even low molecular weight drugs become entrapped therein.Therefore, these excipients are not useful for delivery of bioactivemacromolecules. It is then necessary to incorporate latent catalystadditives with the excipient to enhance hydrolysis in order to free theentrapped drug. Not to mention the biological consequences, theadditives and the fragments formed by the depolymerization of thepolyester will limit the number of drugs that can be compounded with theexcipient materials. The limitation seriously reduces the generalusefulness of these polymers as a potential excipient for drug deliveryimplants. Consequently, in spite of extensive efforts, very few suchexperimental implants have advanced even to the level of testing inlaboratory animals.

At present, there is only one procedure producing a non-absorbablepolymer implant for polypeptide hormone such as insulin which has beenclearly demonstrated to be capable of promoting growth and reducinghyperglycemia for many weeks (Langer et al., Diabetes, 29 (1980) 37). Inthis procedure insulin is mixed with poly-(ethylene/vinyl acetate)copolymer in methylene chloride at sub-zero temperature, and the solventis then slowly evaporated. The resulting slab can be seen under theelectron microscope to contain small pores which allow the diffusion ofinsulin from the polymer implant. Even with this special elaborateprocess, only about 3% of the insulin incorporated will become availablefor reducing hyperglycemia. Since the small pores may be prone toclogging and the poly-(ethylene/vinyl acetate) copolymer is not degradedin the body, the majority of the insulin is trapped by the solid polymerphase without being able to exert its activity. Although the procedureis a remarkable advancement in the technology of sustained actionimplants for insulin, the preparation does not have much practicalsignificance.

In consideration of the aforementioned, an implant containing bioactivemacromolecule should be simple, so that it will be easy to fabricate andrequire no follow-up maintenance when implanted. Its size has to besmall to avoid imposing excessive tension on the subcutaneous tissue dueto stretching when the implant is inserted in the body. The deviceshould be able to hold a sufficient amount of the active protein tosustain the desired therapeutic effect for many weeks. As well, theexcipient component should be absorbable by the body without adverseeffect, so that no time consuming surgical procedure is needed toexplant the depleted device. Further, when the implant stoppedfunctioning after several weeks, the incorporated active ingredientshould be essentially depleted, so that a new absorbable implant can beinserted,.if desired, to continue the therapeutic regimen without anyinterference from residual activity of the previous implant. Finally, itis equally important that no surge of the active ingredient should occurin the body that could cause an overdose and be dangerous to therecipient, if the implant is fractured.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide absorbablepreparations containing bioactive macromolecule capable of sustainedrelease for many weeks.

It is a further object of the present invention to provide preparationscontaining polypeptide hormone for reduction of hyperglycemia and growthpromotion which satisfy one or more of the above criteria.

The present invention provides preparations containing bioactivemacromolecule and an essentially water-insoluble compound in the form oflipoidal fatty substances as the excipient. When implanted, the desiredeffect is achieved, and at the same time the said lipoidal excipient canbe absorbed as well as used by the body without adverse effect. In oneembodiment, the excipient in admixture with bioactive macromolecule iscompressed into a pellet disc or rod, and a portion thereof is implantedsubcutaneously to achieve the desired effect for many weeks. In anotherembodiment, the pellet disc made of a lipid and bioactive macromoleculeis broken up into chips, and a suitable amount is insertedsubcutaneously through the lumen of a large gauge hypodermic needle.

Like other materials aforementioned, lipids have been used to deliverlow molecular weight compounds, such as steroid hormones (Kincl, et al.,J. Pharm. Sci., 66, (1977), 490). These lipoidal substances, beingcomponents of all animal cells and tissues, are varieties ofwater-insoluble compounds. The most abundant kind is the glycerideswhich can be hydrolyzed to yield long-chain fatty acids of negligiblewater-solubility. When these long-chain acids are esterified with theiralcohol derivatives, they form waxes which serve as a protective coatingof the surface tissues. Other members of the saponifiable lipid familyare phospholipids and the sphingolipids found mostly in cell membrane.Among the non-saponifiable lipids, terpenes and most steroids are twoimportant classes. In addition, some steroid-like vitamins are sometimesclassified as lipoidal fatty substances. The most abundant steroid ischolesterol, which is also found in body fluids in combination withlong-chain fatty acids.

For use in the present invention, lipoidal substances which are solid atroom temperature are selected and made into powder form without anyother special treatments aside from grinding in a mortar and pestle fora few minutes. The lipid powder is simply admixed with a suitable amountof bioactive macromolecule, and compressed into a disc or rod withoutany other components. Typical of such solid lipids are saturated fattyacids with 12 or more carbon atoms in the linear chain. The preferredfatty acids are lauric, myristic, palmitic, and stearic acids or acombination of these acids. Their glycerides, as well as similar estersof their unsaturated equivalents, are also solids and readily availablein abundance. However, the esters of these long-chain acids and theircorresponding alcohols are sometimes waxy substances which may behardened and ground at low temperature into the powder form. Polarlipids that can be considered as well include phosphatidylethanolamine,phosphatidylcholine, sphingomyelin, phosphatidylserine,phosphatidylinositol, cardiolipin, galactocerebroside, glucocerebrosideor the like. Among the solid steroid o steroid-like members of the solidlipids, the carotenes, vitamins D and K, cholic acids, coprostanol, andcholesterol are readily available in the powder form. The preferredsteroidal lipid is cholesterol which is practical insoluble in water,can be readily compressed into a coherent mass without any binder, andis not known to have any pharmacological effect in the body or bedeleterious to bioactive macromolecule. It is thus also suitable as anexcipient to be used in the instant invention.

In making the pellet disc or rod, all that is required is to admix a drylipid powder thoroughly with a bioactive macromolecule, and thencompress the resulting admixture in a die. If the lipid powder is merelymelted down, suspended or dissolved in a solvent followed by evaporationto form a slab, the powder of bioactive macromolecule will not disperseevenly with the lipoidal excipient which will also be brittle andfragile to handle. The uneven dispersion may also cause too much of thebioactive macromolecule to be available at one time or too little atanother after implantation. Further, when chips are to be obtained,cutting often leads to excessive fracture or disintegration of the slabmade by melting or solvent casting. There is also the possibility ofinactivation of the bioactive macromolecule by heating or organicsolvent action. However, a pellet disc made by high pressure compressionof the said dry powder admixture at room temperature can be readily cutwith a sharp blade into approximately 1 mm³ pieces

In one embodiment, the preparation is made by adding about 8.5 parts ofa natural lipoidal compound to 1.5 part of a desired bioactivemacromolecule. The powder admixture in a capped plastic vial is furtherplaced on a vortex mixer to ensure thorough mixing, and then carefullytransferred into the well of a 13-mm pellet die to yield a smooth andfirm pellet disc after compression at 2.5 metric tons.

In a preferred embodiment of the present invention, 8 parts of palmiticacid powder is mixed thoroughly on a vortex mixer with 2 parts of powderof a bioactive macromolecule. The powder admixture is compressed at 5metric tons into a pellet disc, as aforementioned, having a total weightof about 200 mg.

In still another embodiment of the present invention, the standard sizepellet disc containing a bioactive macromolecule is cut into chips ofapproximately 1 mm³ in size by a sharp blade. These chips are smallenough to be pushed into the subcutaneous space through the lumen of atrocar needle, thus avoiding the need for implantation by a skinincision as required in the case of the disc.

The pellet discs or the chips thereof, made as just described, willrelease only a negligible amount of a water-insoluble bioactivemacromolecule such as insulin, when immersed in a buffer solution evenover a period of several months. Otherwise, the delivery rate may beassessed in vitro. Scanning electron microscopy shows that the highcompression used to make the pellet disc has fused the powders intolayers of coherent solid mass. However, once implanted, the desiredpharmacological effect of a bioactive macromolecule expected can bereadily observed, because the lipoidal material, though insoluble inwater, is nevertheless a component of cell as well as tissue, and thuscan be gradually eroded in vivo. Therefore, the appropriate amount ofinsulin required daily from the pellet disc of the present invention tolower hyperglycemia to an acceptable level while promoting growth may bedetermined to some extent by trial in vivo using different sizes of theinsulin containing disc. If a lesser amount of the insulin daily isdesired, it can be achieved by implanting a small piece of the standardsize pellet disc which is 13-mm in diameter and 1.5 mm thick. Otherwise,a slightly larger piece may be used to provide more insulin daily, ifrequired. The factors which determine the efficacy of the insulinavailable from the implantable preparation of the present invention arevery complicated and cannot be attributed to release from the implant bysimple diffusion. It is found that when 50-mg fragment of a 200-mgpellet disc with less than 10% insulin in the lipoidal excipient, theimplant shows no effect at all or only occasionally reduceshyperglycemia slightly for a short few days, which is impractical. Whenmuch more than 30% insulin is present therein, the implant may be fatalto the diabetic test animal or again, the reduction in hyperglycemiaoccurs for only several days. The less than optimal performance may bedue to other biological parameters, such as the rate of insulinabsorption by tissue, its inactivation by antibodies and enzymes ininterstitial fluids, fluctuating metabolic demands, etc., that cannot beoverlooked. Because of the variable biological parameters justaforementioned, it is often observed that, for example with 20% insulincontent, very similar level and length of time in hyperglycemiareduction and body weight gains can be achieved when the 1-mm³ chipsequivalent in weight to a quarter piece disc, a 1/8 or 1/4 piece of thewhole pellet disc is implanted. In contrast, when identical pieces ofthe insulin containing implant were inserted in several diabetic animalsof comparable body weight, the length of time observed for hyperglycemiareduction and increase in body weight may be different. But,subcutaneous insertion of three 1/4 pieces of an active pellet disc isgenerally found to be fatal for a diabetic Wistar rat of body weight<400 g. Therefore, in spite of these biological variations, it ispossible to determine a suitable implant size by the bioassay methodjust described which will result in effective reduction i hyperglycemiawhile sustaining growth for several weeks at least, and often exceeding1 month.

The invention is further described by the following specific examples,which are presented as illustrations, and not intended to limit thescope of the present invention.

EXAMPLE 1

An amount of 160 mg of powdered palmitic acid and 40 mg of powderedbovine insulin (24 IU/mg) are first mixed by hand in a 4 cm by 4 cmplastic weighing boat using a stainless steel spatula. The mixed powderis then transferred into a 1.5-mL capacity conical centrifuge tube withcap which is made of polyethylene material. The capped conical vial ispressed onto the platform of a vortex mixer (Vortex-Genie MixerCatalogue number 12-812, Fisher Scientific Co., Toronto) turned to itsmaximum speed. After 2 min. on the mixer, all the well-mixed powder iscarefully tapped from the vial into the well of the Spex 13-mm die (SpexIndustries, Inc., Edison NJ). When the plunger component is properlylowered into the well, the die set is placed in the center between thejaws of the hydraulic press (Spex-Carver Model C, Spex Industries,Inc.). A moderate compression of 0.5 metric ton is first applied beforethe vacuum pump hose is connected to the side of the die set to evacuateits internal chamber. After 2 min of evacuation to remove entrapped airwhich would make the interior porous and reduce cohesion, thecompression is raised to 5 metric tons and held at this level for 5 min.When the vacuum and compression are released, the mid section of the diehousing is unscrewed from its base and the finished pellet disc ispushed from the central well by gently tapping the exposed plunger stem.

The smooth opaque pellet disc is scored in the middle with a small nailfile before it is cut into 2 equal pieces over the groove with a utilityknife. One 1/2 piece of the pellet disc and a plastic coated magneticstirring bar are dropped into 100 mL of phosphate buffered saline at pH7.4 in a 300-mL flask which can be closed with a screw cap. The contentof the flask is stirred gently at room temperature and 0.8 mL of thesolution is taken weekly. The solution sample is mixed with 0.2 mL of aCoomassie G-250 dye reagent (Protein Assay Kit, Cat. No. 500-0006,Bio-Rad Laboratories, Ltd., Mississauga, Ontario) and the intensity ofthe blue-green color is measured at 595 nm. This method has asensitivity of 1 μg protein/mL and is highly reproducible. Analyses overa 6-week period show that less than a total of 10 μg insulin has leachedout, which ensures that no initial burst of the drug will occur uponimplantation to cause any dangerous overdose.

TEST 1

Male Wistar rates weighing 320 to 380 g each are divided into 3 groupswith 1 as healthy control, a second one as diabetic control and a thirdgroup of 2 for testing. Each animal in the second and third group isinjected with 50 mg streptozotocin/kg body weight by the tail vein toinduce diabetes by irreversibly destroying the insulin producing cellsin their pancreas (O. P. Ganda, et al., Diabetes, 25, (1976), 595). Adrop of blood is taken by tail vein puncture from each of the lightlyether-anesthetized animals and smeared evenly over the tip of theDextrostix® (blood glucose test strip made by Miles Lab. Ltd.,Etobicoke, Ontario). Meanwhile, the timer on the Glucometer®(Colorimeter for Dextrostik®, Miles Laboratories) is activated, andafter 60 sec when the alarm has sounded, the blood layer is thoroughlywashed off from the Dextrost®. The intensity of the blue color on thetip is a measure of the blood glucose level in the sample and can bedetermined quantitatively by inserting the developed Dextrostik® intothe Glucometer®, which will show the glucose content on its indicatordisplay in mM glucose/L blood. The results show that the healthy controlhas a range of about 6-11 mM glucose/L blood, while the diabetics have avalue exceeding 22 mM/L on the day after streptozotocin injection, whichis the maximum limit that can be read on the Glucometer®. On the 8th dayafter the induction of hyperglycemia, 1 of the diabetic animals in thethird group is implanted subcutaneously near the abdomen with 1/8 of thestandard size pellet disc prepared as just described. A diabetic rat ofbody weight between 300-400 g requires about 3 IU insulin daily to lowerthe blood glucose level to the normal range of 6-11 mM/L. In the 1/8portion of the standard size pellet disc, there is 5.0 mg insulin or atotal of 120 IU, which should be sufficient to supply the need for 40days. The remaining diabetic animal in the third group is implantedsubcutaneously with 1/4 of the standard size pellet disc. The 1/4 disccontains enough insulin to reduce hyperglycemia for 80 days or almost 3months. The blood sugar level for all 3 groups is monitored atconvenient intervals henceforth. While the blood sample is being takenfrom the lightly anesthetized animal, the presence of the implanteddiscs is checked by palpation and the weight of the animal is alsorecorded. Food and water are made available to all the animals adlibitum. The blood glucose results are summarized in Table 1 shownbelow.

                  TABLE 1                                                         ______________________________________                                        Lowering of Blood Glucose by Insulin Containing                               Preparation Implanted in Diabetic Wistar Rats                                 Blood Glucose (mM/L)                                                          Duration                                                                              1st Group    2nd Group     3rd Group                                  (days)  (Healthy Control)                                                                          (Diabetic Control)                                                                          A*   B**                                   ______________________________________                                         0      9.1          >22           >22  >22                                                            Implanted                                             1      8.2          --            3.5  2.4                                    3      --           --            4.0  3.9                                    5      7.4          >22           2.2  3.0                                    8      --           --            3.0  3.1                                   10      6.5          --            --   --                                    12      5.1          >22           3.3  3.5                                   14      --           --            3.7  3.2                                   16      --           --            3.0  2.2                                   18      6.0          --            4.1  3.0                                   20      --           >22           --   --                                    22      5.7          --            6.5  3.3                                   24      --           --            3.5  3.0                                   26      10.2         --            --   2.7                                   28      --           --            2.9  2.0                                   30      6.1          >22           3.7  3.5                                   32      --                         20.1 4.0                                   34      8.8          --            >22  3.6                                   36      --           --            20.6 4.1                                   38      5.9          >22           >22  3.0                                   40      --           --            --   14.5                                  42      --           --            --   >22                                   44      --           >22           --   >22                                   46      --           --            >22  >22                                   50      6.5          >22           --   >22                                   ______________________________________                                         *1/8 disc                                                                     **1/4 disc                                                               

As shown in the last 2 columns of Table 1, reduction in the bloodglucose level was observed the next day indicating the fast onset ofaction. The test animals also continued to gain weight when checked atthe time of taking blood samples. In the 30-day period, the diabeticanimal with implant in the 3rd Group-A gained 57 g, and the otherdiabetic animal in the 3rd Group-B gained 82 g during the time when theimplant wa functional for about 40 days. The healthy control animal inthe 1st Group gained body weight steadily as expected, but the diabeticcontrol in the 2nd Group lost 45 g after 38 days and it appearedemaciated as well as stunted.

Hyperglycemia recurred on the 32nd day of the calculated 40-day servicelife of the 1/8 disc implanted in the diabetic rat of the 3rd Group-A.For the 1/4 disc in the 3rd Group-B of another diabetic animal, thepreparation implanted functioned well until the 40th day of thecalculated 80-day supply of insulin. Since the blood glucose valuesmonitored over the period were lower than the healthy control group, theimplants in the 3rd Group of diabetic animals might have received morethan the postulated 3 IU/day which would account for the shorter servicelife actually observed. Since the implant in the animal of the 3rdGroup-B was double in size as compared to the other without showing illeffects, the results also demonstrated the margin of safety in the useof the implant. At biopsy to retrieve the implant, no fibrous tissueencapsulation was evident, and the previously distinct edges of theimplant made of palmitic acid was found to have been rounded by erosion.In 1 animal, the spent implant had broken into several small pieces.Analyses by solid phase radioimmunoassay showed that there was onlytrace amount of insulin remaining in the recovered lipid remnants

EXAMPLE 2

An amount of 170 mg cholesterol powder is mixed with 30 mg of bovineinsulin powder (24 IU/mg) and compressed into a pellet disc at 2.5metric tons essentially as described in Example 1. Therefore, thispellet disc contains 15% insulin by weight. The disc is cut evenly into8 pieces, and 2 pieces are inserted subcutaneously near the abdomen ofeach of 3 streptozotocin-induced diabetic Wistar rats of comparable bodyweight. The blood glucose level shown in Table 2 is monitored byDextrost® and the Glucometer®. Food and water are available to theanimals ad libitum.

                  TABLE 2                                                         ______________________________________                                        Reproducibility of Hyperglycemia Reduction                                    by the Pellet Disc Pieces                                                     Duration  Blood Glucose (mM/L)                                                (Days)    1st Rat     2nd Rat  3rd Rat                                        ______________________________________                                        (diabetic with no disc)                                                        0        >22         >22      >22                                            (24 hr after 1/4 disc inserted)                                                1        14.5        2.8      3.4                                             3        5.1         4.4      2.9                                             6        3.0         3.9      4.1                                            10        4.2         11.4     3.0                                            14        3.3         4.1      2.7                                            17        20.3        3.0      2.2                                            20        >22         3.2      21.5                                           23        >22         5.7      >22                                            26        >22         3.2      >22                                            29        --          >22      --                                             32        --          >22      >22                                            35        >22         >22      --                                             ______________________________________                                    

The data demonstrate that there is similar hyperglycemia reduction inall 3 diabetic animals up to day at least. But in the 2nd rat, itcontinued for about 12 more days, and at least 3 extra days for the 3rdrat. Therefore, the pieces from the same pellet disc can providereproducible reduction in hyperglycemia, while the duration may vary indifferent animals. All 3 rats sustained growth in body weight during thefunctional period of the implant. The 1/8 pieces of pellet disc wereretrieved from the diabetic animals after 35 days and analyzed forresidual insulin. After cleaning, the pieces were crushed in 50 ml ofphosphate buffered saline which was warmed to 40° C. to enhance theextraction of the insulin quantitatively. After the appropriate dilutionof this solution, analyses by solid phase radioimmunoassay show thatthere is negligible amount of insulin remaining.

EXAMPLE 3

A 200-mg pellet disc containing 30% bovine insulin in stearic acid, iscut evenly into four 1/4 pieces. Two pieces are then implantedsubcutaneously near the abdomen of an alloxan-induced (200 mg/kg bodyweight) diabetic male New Zealand White rabbit of body weight 3.1 kg andblood glucose content at >22 mM/L for 2.5 weeks. The blood glucose ismonitored the day after insertion of the 1/4 pellet disc, and then inthe intervals shown in Table 3 below. On 2 occasions, the 1/4 pelletdisc implant is taken out then later re-inserted. A normal non-diabeticrabbit has a range of 5.1 to 6.3 mM glucose/L blood when monitored onalternate days in a 2-week period. Food and water are available adlibitum as usual. The changes in blood glucose level with insertion andremoval are given in Table 3.

                  TABLE 3                                                         ______________________________________                                        Dependence of Blood Glucose on the Presence of Insulin-                       Containing Lipid Pellet Disc in Diabetic Rabbit                               Duration          Blood Glucose                                               (days)            (mM/L)                                                      ______________________________________                                        (no disc)                                                                      0                >22                                                         (24 hr after disc inserted)                                                    1                7.8                                                          3                4.7                                                          9                5.8                                                         12                5.0                                                         (removed disc)                                                                13                18.7                                                        14                >22                                                         17                >22                                                         20                >22                                                         (re-insert same disc)                                                         21                6.5                                                         23                5.1                                                         26                4.3                                                         30                4.7                                                         (remove disc again)                                                           31                21.1                                                        32                >22                                                         34                >22                                                         36                >22                                                         (insert same disc again)                                                      38                4.4                                                         41                5.0                                                         45                6.2                                                         50                6.8                                                         ______________________________________                                    

The data presented above unequivocally demonstrate the dependence ofblood glucose change of the diabetic rabbit on the insulin containingpreparation of the present invention. As well, during the alternatingperiod, the body weight of the rabbit was observed to increase when thefunctional implant was in place, but a decrease of as much as 175 g inbody weight could be detected within 24 hr upon removal of the implant.In addition, the activity of the labile insulin in the 1/4 pellet discdoes not seem to be affected by the in vivo and ex vivo alternationproviding that the retrieved pellet disc segment is preserved in asterile container and refrigerated. When the 1/4 pellet disc is in thebody of the diabetic rabbit, normoglycemia is maintained to a remarkableconsistency.

An amount of 150 mg palmitic acid, 20 mg glyceryl tripalmitate, and 30mg porcine insulin (24 IU/mg) are mixed thoroughly in the plasticweighing boat, and then in a capped polyethylene tube on the vortexmixer. The fine powder admixture is compressed into a standard sizepellet disc essentially as described in Example 1, except at 3 metrictons for 5 min. The smooth pellet disc is cut on a Teflon® into chips ofapproximately 1×1×1 mm³ with a utility knife. The chips are picked upindividually with a pair of tweezers and briefly dipped in a smallamount of water to wash off any adhering powder. Several pieces of thechip are transferred to a small plastic weighing boat and about 25 mg ofthe total is taken for subcutaneous insertion near the abdomen of adiabetic Wistar rat (body weight: 350 g) by a trocar needle. The weightof the chips corresponds to about 1/8 of the original standard sizedpellet disc and should have an insulin content of about 4 mg. Thisamount of insulin has a total activity of about 100 IU. At a demand ofabout 3 IU/day, it is expected to reduce hyperglycemia in the diabeticrat for 33 days. The test animal is bled according to the schedule shownin Table 4, and the Glucometer® method is used to determine the glucoselevel as in Example 1.

                  TABLE 4                                                         ______________________________________                                        Lowering of Blood Glucose in Diabetic Rat                                     by Inserted Insulin Containing Chips                                          Duration        Blood Glucose                                                 (days)          (mM/L)                                                        ______________________________________                                        (no chips inserted)                                                            0              >22                                                           (chips inserted)                                                               1              3.0                                                            2              2.4                                                            3              2.7                                                            4              3.0                                                            7              2.8                                                           10              3.8                                                           15              3.1                                                           21              2.9                                                           28              2.9                                                           34              3.2                                                           36              3.4                                                           40              20.1                                                          47              >22                                                           50              >22                                                           ______________________________________                                    

The results obtained show that even when the pellet disc is sub-dividedinto fragments, there is no unexpected overdose of the incorporatedinsulin. The same hyperglycemia reduction is again achieved incomparison to the larger pieces of the pellet disc as described inExample 1. However, the longer duration of maintenance does not appearto be entirely consistent with the data for the 1/8 pellet disc given inTable 1 of Example 1. Th difference further indicates the complexity ofthe on-going process involving erosion, as well as insulin availability,demand, absorption and its inactivation which apparently vary among thetest animals. In addition, the more expensive porcine insulin usedherein is known to be less immunogenic than the similar polypeptidehormone of bovine origin, and perhaps less prone to complexing withantibodies. At biopsy on day 50, only small round remnants of theinserted chips could be found, indicating absorption had occurred.Further, this animal grew by 117 g during the 40-day period of therapy.

EXAMPLE 5

An amount of 110 mg palmitic acid, 20 mg cholesterol, 30 mg stearicacid, and 40 mg porcine growth hormone somatotropin powder is mixedthoroughly and compressed into a pellet disc at 3 metric tons for 3 min.as otherwise outlined in Example 1. The disc is cut into quadrants, anddropped into a stirred flask containing 1 L of bicarbonate buffer at pH8 with 0.1% sodium azide as preservative. Aliquots are withdrawn twiceweekly for analyses of protein content by the Coomassie dye methoddescribed in Example 1. The increasing amount of the polypeptide hormonein the solution is shown in Table 5 below.

                  TABLE 5                                                         ______________________________________                                        Cumulative Amount of Somatotropin                                             in Solution Derived from Pieces of Pellet Disc                                Duration     Hormone in                                                       (days)       Solution (mg/L)                                                  ______________________________________                                         1            1.1                                                              3            3.8                                                              5            6.0                                                              8            9.2                                                             10           10.9                                                             12           13.0                                                             15           17.5                                                             17           18.2                                                             19           21.1                                                             22           25.0                                                             24           26.1                                                             26           27.4                                                             29           31.3                                                             31           34.9                                                             34           36.5                                                             36           36.1                                                             40           36.4                                                             ______________________________________                                    

The results showed that >90% of the polypeptide hormone entered thestirred solution gradually for a period of over 4 weeks. If moresomatotropin is required daily, additional pieces may be used or itscontent in the pellet disc can be slightly increased. For implantationto promote growth, no antigenic problem will develop if the preparationis used in an homologous recipient, especially when the excipientcomponents chosen are natural lipid materials present in all

From the preceding examples, it is thus seen that the objects set forthabove are efficiently attained. Since changes may be made in carryingout the above described process and in the article set forth withoutdeparting from the scope of the invention, it will be understood thatthe above examples are illustrative only, and the invention is notlimited thereto.

I claim:
 1. A process of making a bioerodible preparation with sustainedaction implantation comprising admixing an effective amount of solidbioactive polypeptide with lipid powder, and compressing the resultingadmixture under pressure, with the said lipid powder being selected fromthe group consisting of glycerides, waxes, long-chain fatty acids orsalt, amide of anhydride derivatives thereof, phospholipids,sphingolipids, cerebrosides, terpenes, non-hormonal steroids or acombination thereof.
 2. A process of making a bioerodible preparationwith sustained action which reduces diabetic hyperglycemia continuouslyand promotes growth, comprising admixing insulin powder with a lipidpowder, and compressing the resulting admixture under pressure in a die,with the said lipid powder being selected from the group consisting ofglycerides, waxes, long-chain fatty acids or salt, amide or anhydridederivatives thereof phospholipids, sphingolipids, cerebrosides,terpenes, nonhormonal steroids or combination thereof.
 3. A process ofclaim 2 wherein the amount of insulin is about 11% to about 40% byweight of said admixture.
 4. A process of claim 3 wherein the lipid is aglyceride selected from the group consisting of glyceryl esters oflauric, myristic, palmitic, stearic, oleic, linoleic acids orcombination thereof.
 5. A process of claim 3 wherein the lipid is along-chain fatty acid or derivative selected from the group consistingof lauric, myristic, palmitic, stearic, oleic, linoleic acids, theirsimple esters, salts, amides, anhydrides, or combination thereof.
 6. Aprocess of claim 3 wherein the lipid is a non-hormonal steroid selectedfrom the group consisting of coprostanol, cholesterol, cholic acid,their esters, simple glycosides or combination thereof.
 7. A method ofsustaining the action of bioactive macromolecule preparation forimplantation which comprises of compressing a powder admixtureconsisting essentially of effective amount of bioactive polypeptide andlipid powder selected from the group consisting of glycerides, waxes,long-chain fatty acids or salt, amide or anhydride derivatives thereof,phospholipids, sphingolipids, cerebrosides, terpenes, non-hormonalsteroids or combination thereof.
 8. A method of sustaining the action ofbioactive macromolecule preparation for implantation as claimed in claim7 wherein the bioactive macromolecule is insulin.
 9. A method ofsustaining the action of bioactive macromolecule preparation as claimedin claim 8 wherein the amount of insulin is 11% to 40% by weight of saidadmixture.
 10. A method of sustaining the action of bioactivemacromolecule preparation as claimed in claim 9 wherein the lipid is aglyceride selected from the group consisting of glyceryl esters oflauric, myristic, palmitic, stearic, oleic, linoleic acids orcombination thereof.
 11. A method of sustaining the action of bioactivemacromolecule preparation as claimed in claim 9 wherein the lipid is along-chain fatty acid or derivative selected from the group consistingof lauric, myristic, palmitic, stearic, oleic, linoleic acids, theirsimple esters, salts, amides, anhydrides or combination thereof.
 12. Amethod of sustaining the action of bioactive macromolecule preparationas claimed in claim 9 wherein the lipid is a non-hormonal steroidselected from the group consisting of coprostanol, cholesterol, cholicacid, their esters, simple glycosides or combination thereof.
 13. Aprocess of claim 1 wherein said bioactive macromolecule is somatotropin.14. A process of claim 13 wherein the amount of somatotropin comprisesabout 1% to about 50% by weight of said admixture, and the lipid isselected from the group consisting of glyceryl esters of lauric,myristic, palmitic, stearic, oleic, linoleic acids or combinationthereof; lauric, myristic, palmitic, stearic, oleic, linoleic acids,their simple esters, salts, amides, anhydrides, or combination thereof;and coprostanol, cholesterol, cholic acid, their esters, simpleglycosides or combination thereof.
 15. A method of sustaining the actionof bioactive macromolecule preparation as claimed in claim 7 wherein thebioactive macromolecule is somatotropin.
 16. A method of sustaining theaction of bioactive macromolecule preparation as claimed in claim 15wherein the amount of somatotropin is about 1% to about 50% by weight ofthe admixture and the lipid is selected from glyceryl esters of thegroup consisting of lauric, myristic, palmitic, stearic, oleic, linoleicacids or combination thereof; lauric, myristic, palmitic, stearic,oleic, linoleic acids, their simple esters, salts, amides, anhydrides,or combination thereof; and coprostanol, cholesterol, cholic acids,their esters, simple glycosides or combination thereof.
 17. A process asclaimed in claim 1 wherein the lipid is palmitic acid.
 18. A process ofmaking a bioerodible preparation with sustained action which is suitablefor implantation comprising admixing a combination consistingessentially of an effective amount of solid bioactive polypeptide andlipid powder, and compressing the resulting admixture under pressure,with the said lipid powder being selected from the group consisting ofglycerides, waxes, long-chain fatty acids or salt, amide or anhydridederivatives thereof, phospholipids, sphingolipids, cerebrosides,terpenes, non-hormonal steroids or a combination thereof.